1. Field of Invention
The present invention relates to cutting with radiation and more particularly to cutting multilayered sheet material with a beam of laser radiation.
2. Description of the Prior Art
Over the years various devices using energetic beams for cutting and welding have been discussed in the technical literature and the patent art. Some of the early work involved cutting metals with electron beams and laser radiation. Such systems were found useful in particular applications although they have not been universally adopted because of various shortcomings. One of the improvements to cutting with beams of energy was the application of an assist gas jet to the cut zone to aid the cutting process. The jet tends to blow molten material away from the cut zone and, if a reactive gas is used the cutting procedure can be enhanced by chemical reaction between the gas and the workpiece. Such techniques are typified by the teachings in U.S. Pat. No. 3,569,660 entitled Laser Cutting Apparatus issued Mar. 9, 1971 to P. T. Houldcroft and U.S. Pat. No. 3,597,578 entitled Thermal Cutting Apparatus And Method issued on Aug. 3, 1971 to A. B. Sullivan et al. The cutting art developed and became more sophisticated allowing beams of radiation to be used for various forms of materials processing. One of the persistent shortcomings which workers in the field encounter is the inability to produce a uniformly smooth clean cut due to excessive or improperly distributed energy during the materials processing. Deleterious effects such as scorching, sticking and globularizing along a cut pattern have been minimized and in some cases eliminated by the application of a coolant, usually in the form of a gas, or mist or some combination thereof. A typical teaching in this regard is provided in U.S. Pat. No. 3,629,546 entitled Air-Cool Laser Processing Of Materials issued to F. H. Fry on Dec. 21, 1971. Additional material which is representative of the state of the art as typified in Fry is disclosed in The CO.sub.2 Laser And Its High Power Applications by M. Hillier, Design Engineering, May 1969, page 47 and Laser Welding And Cutting by M. M. Schwartz, Welding Research Council Bulletin 167, November 1971. An outgrowth of these disclosures occurs in U.S. Pat. No. 3,679,863 entitled Thermal Cutting Apparatus issued to P. T. Houldcroft on July 25, 1972. The patent teaches the cutting of materials such as paper and fabric with a laser beam utilizing a jet of gas which is inert with respect to the process to carry an atomized stream of liquid coolant into the region of the cutting activity at the workpiece to reduce the charring which is otherwise observed. Although several patents and technical publications describe the use of laser radiation to cut various materials including metal, plastic, wood, composites, fiber and synthetic material, no one has reported successful cutting of a layered stack of sheet material having a low melting temperature without incurring various degrees of sticking together of the adjacent layers of the material being cut.